Galvanic anodes are electrically connected to steel reinforced concrete structures to protect the steel from corrosion. In the course of protecting the steel to which they are attached, galvanic anodes can expand due to the formation of corrosion products from the sacrificial metal, which is usually zinc. In severe cases, such expansion can cause the buildup of stresses within the concrete in which the galvanic anode is buried. Such stresses can compromise the integrity of the concrete covering causing it to crack or rupture.
Another problem with large galvanic anodes, and particularly planar galvanic anodes, is caused by differential expansion and contraction between active galvanic layers within the anode and the support substrates and/or with respect to the base concrete to which such panel-shaped anodes are attached. This expansion and contraction can cause the layered galvanic anode construction to distort or warp, compromise its internal physical integrity and/or cause disruption of the bond between a backing substrate and active galvanic material or with the base concrete to which such anodes are attached. Such expansion, contraction and warpage can be caused by many factors such as differential drying rates between layers within the anode during manufacture or use and/or the buildup of corrosion products in operation.
The incorporation of a stress relieving compliant layer in the laminated manufacture of large planar supported galvanic anode panels allows the panels to stay perfectly flat and/or free of warpage and distortion no matter what the degree of differential expansion/contraction between substrate and anode portions of the composite product.
The compliant layer also imparts a degree of sound deadening and sound insulation to the finished panel.
Previous attempts to solve the cracking and warping problem associated with the fabrication and use of large galvanic anode panels have been directed at forcefully restraining any such expansion by the use of high strength reinforcing layers that bind the active portion of the anode in such a way that the expansion forces are prevented from compromising the adhesion to or structural integrity of the concrete within or against which such anodes are used.
These problems are addressed and solved below without forceful restraint with the use of a compressible, compliant and/or spongy layer of material interposed between the active galvanic anode portion of the overall construction and the supporting carrier or substrate which can form part of the construction. The substrate can take the form of a fiberboard or concrete or mortar “backer board” commercially available in the form of flat planar rectangular panels in sizes several feet on a side, similar to plywood panels.
The compliant, compressible or spongy layer can also be used between galvanic anodes and the concrete structure containing the steel which is to be protected, as long as provision is made for the passage of ions through the compliant, compressible or spongy layer. Such ionic passage can be an intrinsic property of the compressible layer such as natural materials like paper products or provided with additives such as humectants, deliquescents or water absorbers which can be incorporated into the compliant layer to render it ionically conductive.
The compliant, compressible and/or spongy layer in this new galvanic panel construction can be a layer of soft plastic or rubber sponge or foam, or a sheet of a woven, a nonwoven or flocked fabric, such as felt. In one embodiment, a needle-punched nonwoven fabric is used. For good results, the construction of the fabric is ideally “lofty” with good spacing and void spaces between fibers and/or air cells and not too dense. The compliant, compressible or spongy layer is bonded into the construction by a galvanic mortar applied between it and the substrate on one side and between the compliant, compressible and/or spongy layer and the galvanic anode mortar containing the galvanic metal anode on the other side.
The thickness of the compliant, compressible and/or spongy layer and the viscosity or composition of the surrounding mortar or adhesive, plus the degree of mechanical compaction in the manufacturing process are chosen to be such that the galvanic mortar and adhesive penetrates or adheres partially into or onto the face of the compliant material from both sides. The penetration is ideally sufficient to develop a sound mechanical bond between the mortar and each facing of the compliant, compressible and/or spongy layer once the mortar and adhesive has dried and cured but not so much that the mortar or adhesive penetrates entirely through the compliant media. This results in a central or interior portion of the compliant, compressible and/or spongy layer remaining unfilled with mortar leaving an open air filed layer which allows for this layer to compressively absorb any stresses or movement between layers of the anode construction, however caused. In one embodiment, the compliant, compressible or spongy material can be about 1/16 to ¼ inch thick.
This construction can be used to make large flat stress-free supported galvanic anode panels for use on virtually any reinforced concrete structures, such as building walls and floors, concrete decks and pilings, parking structures and the like. If desired, the support or substrate of the laminated panel construction can be provided with an external decorative surface or painted or otherwise formed with decorative or functional embossed patterns or text.